Solar DNA tests detect cancer without electricity

The power of the sun could spark a medical revolution. A device can diagnose diseases using nothing more than a smartphone, sunlight and a tiny DNA sample.

The KS-Detect, built by engineers at Cornell University in New York, will be used to diagnose Kaposi’s sarcoma, the AIDS-related cancer that killed Tom Hanks’s character in the film Philadelphia. Li Jiang and his colleague David Erickson, are now testing the KS-Detect in Uganda, in partnership with Makerere University in Kampala.

Kaposi’s sarcoma is one of the most common forms of cancer across sub-Saharan Africa, caused by a herpes virus that takes advantage of weakened immune systems. It kills between a fifth and a third of those it infects within a year – and up to 70 per cent within three years. Late diagnosis of the disease is one of the main factors contributing to the low survival rate. Cornell’s KS-Detect aims to change this.

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Testing for the disease typically involves using the polymerase chain reaction (PCR) to amplify traces of the herpes virus DNA in the presence of a primer, a bit of DNA which binds to pre-selected target sequences and serves as the starting point for the strand to be copied. This process is repeated until there are enough copies to show up in a detector. Normally, precision electronics are needed to heat and cool the sample and drive the reaction.

Disc of light

The KS-Detect works without electricity by using a lens to focus the sun’s rays into a disc of light where the edges are cooler than the centre. A long microscopic channel is etched onto a chip that is placed under the disc of light. The sample moves along this channel so that its temperature changes in cycles, alternating between the heat at the centre of the light disc, and the cool edges.

This drives the PCR. A dye called SYBR Green glows under blue light if amplified DNA from the herpes virus is detected. A smartphone controlling the chip then reads the results.

“We thought why not go straight to the source and use sunlight directly as heat, skip the electricity?” says Jiang. “That let us skip a lot of the components you need in normal PCR.”

Francis Moussy of the World Health Organization in Geneva, Switzerland, is impressed. With such a device people can be tested where they live. “It’s really important to bring diagnostics to the patients instead of making the patients travel,” he says.

Moussy, who works on new kinds of medical diagnostic technology for the WHO, says the researchers’ device can be adapted to detect other diseases. All that is needed is to change the primers so that different kinds of DNA can be amplified. “PCR is used for the detection of TB [and] can be used for many non-communicable diseases. It’s a tool that’s becoming more and more useful.”